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meynaf · 18 August 2016, 07:34

A branch with $FE is likely to be a quick'n'dirty error handling, so it has better be predicted as not taken. Hey, wait -- it's a backward branch so default would be taken and it needs the hint bit to reverse that...

So now we have :
- $FE unable to get the hint bit (and always mispredicted)
- $01 useless
- BRA and BSR not using the hint bit
- the hint bit moves away in case of larger branches
Who told about 'special cases' ?

18 August 2016, 07:34	#77
meynaf son of 68k Join Date: Nov 2007 Location: Lyon / France Age: 51 Posts: 5,354	A branch with $FE is likely to be a quick'n'dirty error handling, so it has better be predicted as not taken. Hey, wait -- it's a backward branch so default would be taken and it needs the hint bit to reverse that... So now we have : - $FE unable to get the hint bit (and always mispredicted) - $01 useless - BRA and BSR not using the hint bit - the hint bit moves away in case of larger branches Who told about 'special cases' ?